Apparatus for controlling brake of vehicle

ABSTRACT

An apparatus for controlling the brake of a vehicle, which easily brings the vehicle to a halt, or starts it, only by the action of the accelerator without operating the brake pedal. Brakes ( 4,5 ) are applied when the vehicle speed detected by a speed detector ( 9 ) becomes a predetermined threshold value or less. The operation of the brakes ( 4,5 ) is turned off when a load detected by a load detector ( 10 ) becomes larger than a load operated by a load computer ( 11,14 ).

TECHNICAL FIELD

The present invention relates to an apparatus for controlling a brake ofvehicle which by virtue of automatic control of the on-and-off action ofthe brake serves to relieve the onus on the operator in stopping andstarting the vehicle by compound operation of the accelerator and brakepedals.

BACKGROUND ART

Stopping and starting a vehicle by manual operation of the acceleratorand brake pedals involves subtle handling of these pedals (and also ofthe clutch pedal), and requires the brake pedal to be depressedconstantly while the vehicle is at a standstill. It thus demands a fairdegree of experience on the part of the operator, while the onus on himis great. This is particularly true when stopping and starting on ahill.

For this reason there has long been a demand to facilitate the stoppingand starting of a vehicle by means of a simple operation which places aslittle onus as possible on the operator.

Japanese Patent Application Laid-Open No. 59-143746 proposes holding orreleasing braking force by means of controlling an electrically operatedparking brake device.

In other words, according to the abovementioned invention, if withvehicular speed at zero the accelerator pedal is released and the brakepedal depressed, the parking brake device operates and stops the vehicleautomatically.

This means that if, for instance, an attempt was made to exert subtlecontrol over the vehicle by operating only the accelerator pedal with aview to maintaining a safe distance from a vehicle in front on a steepupward slope, it might in the end become necessary to depress the brakepedal, and the vehicle would sometimes begin to move backwards beforethis operation was effected.

Moreover, in the abovementioned invention, the engine rotational speedat which it is possible to obtain the output necessary to ensure thatthe vehicle does not roll backwards on a slope is set in accordance withthe gradient of the slope, so that the parking brake is released and thevehicle allowed to move forward once the engine attains a speedcorresponding to the gradient of the slope as detected by a gradientsensor.

It is true that in vehicles which employ torque converters the tractiveforce is more or less determined by the engine rotational speed and thespeed stage, and that releasing the brake when the engine has attained aspeed corresponding to the current gradient does not create any problembecause the necessary tractive force can be obtained. However, invehicles which employ direct transmission the tractive force isdetermined by the transmission torque of the main clutch, and not by theengine rotational speed. Moreover, much the same applies also tovehicles which employ other types of transmission and to vehicles drivenby electricity, where again the tractive force is not determined on thebasis of the engine rotational speed.

Accordingly, in vehicles of this sort it does not follow that therequired tractive force can always be obtained even if the engine hasattained a speed corresponding to the current gradient when the brake isreleased.

For this reason there has been a tendency for the tractive force onbrake release either to be insufficient, so that the vehicle begins toroll backwards, or to be too great, with the result that the tires slip.

Japanese Patent Application Laid-Open No. 61-200054 similarly proposes atechnique for holding or releasing braking force by means of controllingthe hydraulic brakes.

That is to say, according to the abovementioned invention, when thegradient (inclined angle) of the vehicle is at a given standard value ormore, the foot-brake is applied and the vehicle speed is zero, acylinder pressure becomes greater than a brake-holding pressurecorresponding to the gradient. When the hydraulic pressure falls againand matches the holding pressure, a control valve closes, brake pressureis held, and the brake operates.

In this manner, the fact that the abovementioned invention presupposesthat “applying the foot-brake” is an automatic braking action means thatas in the case of Japanese Patent Application Laid-Open No. 59-143746there has been a tendency for the vehicle to begin rolling backwardsbefore the brake pedal is finally depressed.

Moreover, in the abovementioned invention the control valve and brakeare released when the degree of opening of the accelerator is greaterthan a given standard value and the clutch switch is on. Thus, inasmuchas it does not assess whether or not the tractive force corresponds tothe current gradient of the road, there has been a tendency on steepgradients for vehicles to begin rolling backwards as soon as the brakeis released.

DISCLOSURE OF THE INVENTION

It is a first object of the present invention, which has been designedwith these circumstances in mind, to allow a vehicle to be brought to ahalt in a simple manner by depressing only the accelerator and withoutdepressing the brake pedal, and to ensure that this is accomplishedwithout the inconvenience of the vehicle beginning to roll backwards.

It is a second object of the present invention to ensure that it ispossible to start the vehicle on a slope without any difficulty and witha tractive force corresponding to the gradient irrespective of the typeof transmission, and even when applied to vehicles of types other thanthose which are driven by an engine.

In order to accomplish the first object, a principal aspect of thepresent invention is an apparatus for controlling a brake of a vehiclehaving an accelerator pedal and a brake pedal, comprising:

traveling speed detecting means for detecting a travelling speed of thevehicle; and

control means for controlling to actuate the brake when the travellingspeed detected by the travelling speed detecting means becomes aprescribed threshold value or lower.

In this manner, the brakes are applied automatically by virtue of thefact that the speed of the vehicle has fallen below a certain value,thus allowing the vehicle to be brought to a halt in a simple manner bydepressing only the accelerator and without depressing the brake pedal,and to ensure that this is accomplished without the inconvenience of thevehicle beginning to roll backwards.

Meanwhile, in order to accomplish the second object, another principalaspect of the present invention is an apparatus for controlling a brakeof a vehicle having an accelerator pedal and a brake pedal wherein thebrake is automatically actuated and thereafter turned off, comprising:

acceleration detecting means for detecting an acceleration of thevehicle in a forward and backward direction;

load calculating means for calculating, on the basis of the accelerationdetected by the acceleration detecting means, a load on an output shaftwhile the brake is not applied;

load detecting means for detecting the load on the output shaft; and

control means for controlling to turn off the brake when the loaddetected by the load detecting means becomes greater than the loadcalculated by the load calculating means.

In this manner, the brakes are automatically released if the currentload becomes greater than the one which corresponds to the accelerationof the vehicle in a forward and backward direction, thus making itpossible to start the vehicle on a slope without any difficulty and witha tractive force corresponding to the gradient irrespective of the typeof transmission, and even when applied to vehicle of types other thanthose which are driven by an engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of an embodiment ofthe apparatus for controlling a brake of a vehicle to which the presentinvention pertains;

FIG. 2 is a block diagram illustrating an example of an embodiment ofthe apparatus for controlling a brake of a vehicle to which the presentinvention pertains;

FIG. 3 is a block diagram illustrating an example of an embodiment ofthe apparatus for controlling a brake of a vehicle to which the presentinvention pertains;

FIG. 4 is a control block diagram clarifying details of the controladopted in the apparatus illustrated in FIGS. 1-3;

FIG. 5 is a control block diagram clarifying details of the controlwhich is suitable for the apparatus illustrated in FIG. 2;

FIG. 6 is a control block diagram clarifying details of the controlwhich is suitable for the apparatus illustrated in FIG. 3;

FIG. 7 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4;

FIG. 8 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4;

FIG. 9 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4;

FIG. 10 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4;

FIG. 11 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4;

FIG. 12 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4; and

FIG. 13 is a diagram clarifying details of partial modifications to theprocessing in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

There follow, with reference to the drawings, descriptions of severalembodiments of the apparatus for controlling vehicle brakes to which thepresent invention pertains.

FIG. 1 is a block diagram illustrating the configuration of a vehicle towhich the present invention is applied.

As is depicted in FIG. 1, this vehicle runs with an engine 1 as itssource of driving power, and the configuration is such that the drivingpower of the engine 1 is transmitted by way of a transmission 2 and adifferential 3 to left and right tires 6, 7.

On the output shaft of the transmission 2 is located an output shaftrotational speed sensor 9 which detects the rotational speed nO of theoutput shaft. The detection signal nO of this sensor 9 is output to acontroller 14.

Similarly, on the output shaft of the transmission 2 is located anoutput shaft torque sensor 10 which detects the torque τO of the outputshaft. The detection signal τO of this sensor 10 is output to thecontroller 14.

In a suitable position on the body of the vehicle is also located aforward and backward acceleration sensor 11 which serves to detectacceleration a of the vehicle in a forward and backward direction. Thedetection signal α of this sensor 11 is output to the controller 14.

A select lever is provided within the cab of the vehicle, by operatingwhich it is possible to designate and select forward, reverse andneutral. This select lever has a select lever displacement sensor 13which detects the selected position s. The detection signal s of thissensor 13 is output to the controller 14.

The engine 1 of this vehicle is driven by operating an accelerator pedal(not depicted in the drawing) which is located within the cab, and in asimilar fashion the brakes 4, 5 are operated by depressing a brake pedal(not depicted in the drawing) which is also located within the cab.

The brakes 4,5 are controlled automatically by the controller 14 and abrake control actuator 15.

In other words, the output signals nO, τO, α, s from each of theabovementioned sensors are input into the controller 14. Here,calculations and processing as described later are effected, as a resultof which a brake control signal B is output to the brake controlactuator 15.

The brake control actuator 15 feeds on/off control hydraulic pressure inaccordance with the content of the input brake control signal B to thebrakes 4,5 which are located on the left and right wheels. As aconsequence, the brakes 4,5 are applied or released in accordance withthe on/off control hydraulic pressure.

The configuration of the vehicle in which the present invention isadopted may also be that which is depicted in FIG. 2.

As may be seen from FIG. 2, this vehicle is driven by means of a motor19 with a battery 1′ as a source of power, and the driving power of themotor 19 is transmitted by way of the differential 3 to the left andright tires 6, 7.

Those codes which are the same as those used in FIG. 1 refer to the samestructural elements, and their descriptions will not be repeated here.It should be noted that the output shaft rotational speed sensor 9 andthe output shaft torque sensor 10 are located on the output shaft of themotor 19.

In this vehicle, the motor 19 is driven by operating an acceleratorpedal which is located within the cab, while a brake pedal also locatedwithin the cab serves to apply the brakes 4, 5.

On the accelerator pedal is located an accelerator pedal displacementsensor 12 which detects changes in the displacement x of the acceleratorpedal, the detection signal x being output to the controller 14.

The brakes 4, 5 are controlled automatically by the controller 14 andthe brake control actuator 15, as in FIG. 1.

That is to say, the output signals nO, τ, α, s, x from theabovementioned sensors are input to the controller 14, wherecalculations and processing as described later are effected, as a resultof which a brake control signal B is output to the brake controlactuator 15.

The calculations and processing which are effected by the controller 14allow the target rotational speed NO of the motor output shaft to bedetermined, and this target rotational speed NO is output to an invertercontroller 21.

In this manner, not only are the brakes 4, 5 applied or releasedautomatically in response to the brake control signal B output from thecontroller 14, but the inverter 20 is controlled in accordance with thetarget rotational speed NO which is also output from the controller 14.In other words, a control signal corresponding to the target rotationalspeed NO input to the inverter controller 21 is output to the inverter20, and the inverter 20 modifies the drive voltage frequency of themotor 19 in response to this control signal, matching the rotationalspeed of the output shaft of the motor 19 to the target rotational speedNO.

The configuration of the vehicle in which the present invention isadopted may also be that which is depicted in FIG. 3.

As may be seen from FIG. 3, this vehicle is driven by means of a motor19 with a generator 16 driven by the engine 1 as a source of power, andthe driving power of the motor 19 is transmitted by way of thedifferential 3 to the left and right tires 6, 7.

Those codes which are the same as those used in FIGS. 1 and 2 refer tothe same structural elements, and their descriptions will not berepeated here. It should be noted that the output shaft rotational speedsensor 9 and the output shaft torque sensor 10 are located on the outputshaft of the motor 19.

In addition, the output shaft of the engine 1 has located on it anengine rotational speed sensor 8 which detects the rotational speed nEof that shaft, the detection signal nE of this sensor 8 being output tothe controller 14.

In this vehicle, the motor 19 is driven by operating an acceleratorpedal which is located within the cab, while a brake pedal also locatedwithin the cab serves to apply the brakes 4, 5.

Moreover, the brakes 4, 5 are controlled automatically by the controller14 and the brake control actuator 15, as in FIGS. 1 and 2.

That is to say, the output signals nO, τ, α, s, x, nE from theabovementioned sensors are input to the controller 14, wherecalculations and processing as described later are effected, as a resultof which a brake control signal B is output to the brake controlactuator 15.

The calculations and processing which are effected by the controller 14allow the target rotational speed NO of the motor output shaft to bedetermined, and this target rotational speed NO is output to an invertercontroller 21.

In addition, the calculations and processing which are effected by thecontroller 14 allow the target rotational speed NE of the engine outputshaft to be determined, and this target rotational speed NE is output toa converter controller 18.

In this manner, not only are the brakes 4, 5 applied or releasedautomatically in response to the brake control signal B output from thecontroller 14, but the inverter 20 is controlled in accordance with thetarget rotational speed NO which is also output from the controller 14,while the converter 17 is controlled in accordance with the targetrotational speed NE which is again output from the controller 14. Inother words, a control signal corresponding to the target rotationalspeed NE input to the converter controller 18 is output to the converter17, and in response to this control signal the converter 17 adjusts theelectric power supplied from the generator 16 and drives the generator16 as a motor, matching the rotational speed of the output shaft of theengine 1 to the target rotational speed NE.

It should be added that the abovementioned vehicle is assumed to be onewherein two drive wheels are located left and right, as in afour-wheeled vehicle, but the present invention may also be applied to aone-wheel drive vehicle such as a motor-cycle. It goes without sayingthat it is not restricted to a vehicle which runs on wheels, and mayalso be applied to one which runs on crawler tracks.

Moreover, the output shaft rotational speed sensor 9 is used to detectthe speed of the vehicle against the ground, and in particular lowspeeds, and it may be replaced with a sensor which is capable ofdetecting speeds other than the rotational speed nO of the output shaft.

Similarly, the output shaft torque sensor 10 is used to detect thetractive force of the vehicle, and it may be replaced with a sensorwhich is capable of detecting torque other than the torque τO of theoutput shaft. For instance, where the wheels are driven by the motor,the torque of the motor is proportional to the current supplied, so thata sensor which detects this current can be used to detect tractiveforce.

The forward and backward acceleration sensor 11 is used in order todetect the external force (gravity) to which the body of the vehicle insubjected in a forward and backward direction, and it can be replaced bya sensor which is capable of detecting external force other than forwardand backward acceleration α

What is more, in FIGS. 1-3 manual and automatic brakes form the commonbrakes 4, 5, but they may also be provided separately.

There now follows, with reference to FIG. 4, a description of thecalculations and processing which are effected by the controller 14illustrated in FIGS. 1-3.

In the explanation which follows, the rotational speed nO of the outputshaft assumes a positive value in forward, and a negative value inreverse. In the same way, the torque τO of the output shaft assumes apositive value in forward, and a negative value in reverse.

As may be seen from FIG. 4, to begin with, data from the abovementionedsensors 9, 10, 11, 13 (ie rotational speed no and torque τO of theoutput shaft, forward and backward acceleration α, selected position sof the select lever) is introduced item by item into the controller 14(Step 101).

If it is here assumed that the vehicle is ascending a slope and stops inthe course of the slope, the operator releases the accelerator pedal andapplies the brake (depresses the brake pedal) in order to stop thevehicle.

Here, if the vehicle is in forward mode, that is, if the selectedposition s of the select lever is “forward”, while the content of thebrake control signal B is “off”, the output shaft speed nO is lower thanthe prescribed threshold value NO1 and gradually decreasing, it isjudged that the vehicle may be about to stop, and a brake control signalB with the content “on” is generated (Step 102). This is output from thecontroller 14 to the brake control actuator 15 (Step 105), and thebrakes 4, 5 are applied automatically (Step 106). As a result, theoperator is able to bring the vehicle to a halt on a slope by means ofthe simple operation of releasing the accelerator, although in order todecrease the speed of the vehicle the operator must depress the brakepedal until moments before the vehicle comes to a standstill. Moreover,the vehicle can be kept at a standstill thereafter without the need tocontinue depressing the brake pedal.

In Step 102 above, “when the output shaft speed nO is graduallydecreasing” refers to a state wherein, “the rotational speed nO asdetected by the output shaft rotational speed sensor 9 is lower than thepreviously detected rotational speed n′O”. If this state is confirmed asa result of at least two detections, it can be judged that the operatorhas released the accelerator with the intention of bringing the vehicleto a halt.

The abovementioned prescribed threshold value NO1 is preferably a verylow speed close to zero (eg 1 km/h or less).

Meanwhile, if the vehicle is in reverse mode, ie if the selectedposition s of the select lever is “reverse”, the conditions under whichthe content of the brake control signal changes to “on” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the rotational speed nO of the output shaft assumes anegative value (Step 102).

Furthermore, if the vehicle is in neutral mode, ie if the selectedposition s of the select lever is “neutral”, while the content of thebrake control signal B is “off” and the absolute value of the outputshaft speed nO is lower than the threshold value NO1, a brake controlsignal B with the content “on” is generated (Step 102). This is outputfrom the controller 14 to the brake control actuator 15 (Step 105), andthe brakes 4, 5 are applied automatically (Step 106).

Next, if it is assumed that the vehicle is about to start on a slope,the operator depresses the accelerator pedal in order to start thevehicle.

What happens then is that the load torque τO(α) on the output shaft whenthe brakes are not applied is calculated on the basis of theacceleration α as detected by the forward and backward accelerationsensor 11 (Step 103).

The abovementioned load torque O(α) is the torque which the output shaftreceives from the brake side, and is positive where the vehicle isstarting in an uphill direction.

Meanwhile, the current torque τO on the output shaft is obtained as theoutput of the output shaft torque sensor 10. Here, the load torque τOsignifies the torque which the output shaft receives as counterforcefrom the brake side when the driving power is transmitted to the brakes.It is positive where the vehicle is driven in forward mode.

Now, if these torques TO(α), τO are compared, and in forward mode thecontent of the brake control signal B is “on”, while the output shafttorque τO is greater than the load torque TO(α) corresponding to theabovementioned acceleration, it is judged the brakes can be released inorder for the vehicle to start, whereupon a brake control signal B withthe content “off” is generated (Step 104). This is output from thecontroller 14 to the brake control actuator 15 (Step 105), and thebrakes 4, 5 are released automatically (Step 106). As a result, theoperator is able to start the vehicle with sufficient tractive force forthe gradient of the slope by means of the simple operation of depressingthe accelerator.

Meanwhile, if the vehicle is in reverse mode, the conditions under whichthe content of the brake control signal changes to “off” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the codes for the torque τO, TO(α) are reversed (Step103).

There now follows, with reference to the control block diagram in FIG.5, a description of the most suitable processing for the vehicleillustrated in FIG. 2.

As may be seen from FIG. 5, to begin with, data from the abovementionedsensors 9, 10, 11, 13, 12 (ie rotational speed nO and torque τO of theoutput shaft, forward and backward acceleration α, selected position sof the select lever, changes in accelerator pedal displacement x) isintroduced item by item into the controller 14 (Step 201).

Next, a function f with the current rotational speed nO of the outputshaft, selected position s of the select lever, changes in acceleratorpedal displacement x and time elapsed t as variables is used tocalculate the target value NO=f (x, t, nO, s) of the rotational speed ofthe output shaft of the motor 19. This target value NO assumes apositive value in forward mode and a negative value in reverse mode. Theminimum value NOmin in forward mode and the maximum value NOmax inreverse mode are 0.

The target rotational speed NO of the output shaft calculated in thismanner is output to the inverter controller 21 (Step 202). As a result,the motor 19 is controlled via the inverter controller 21 in such amanner that the rotational speed of the motor 19 becomes theabovementioned target rotational speed NO. In this process the output nOof the output shaft rotational speed sensor 9 is used as the feedbackamount (Step 207).

If it is here assumed that the vehicle is ascending a slope and stops inthe course of the slope, the operator releases the accelerator pedal andapplies the brake (depresses the brake pedal) in order to stop thevehicle.

Here, if the vehicle is in forward mode, ie if the selected position sof the select lever is “forward”, while the content of the brake controlsignal B is “off”, the output shaft speed nO is lower than theprescribed threshold value NO1, and the output shaft torque τO isgreater than the prescribed threshold value TO1, it is judged that thevehicle may be about to stop, and a brake control signal B with thecontent “on” is generated (Step 203). This is output from the controller14 to the brake control actuator 15 (Step 206), and the brakes 4, 5 areapplied automatically (Step 207). As a result, the operator is able tobring the vehicle to a halt on a slope by means of the simple operationof releasing the accelerator, although in order to decrease the speed ofthe vehicle the operator must depress the brake pedal until momentsbefore the vehicle comes to a standstill. Moreover, the vehicle can bekept at a standstill thereafter without the need to continue depressingthe brake pedal.

In Step 203 above, the reason for the condition that “the output shafttorque τO is greater than the prescribed threshold value TO1” is asfollows.

In the case of a vehicle which is driven by a motor, it is possible tostop on a slope while maintaining tractive force by making the targetspeed 0, and there is consequently no need to apply the brakes. However,if the slope is steep, the electric current flowing to the motorincreases, with resultant loss of energy. In such circumstances thebrakes are applied and the motor current reduced to 0 in order to reduceenergy loss.

Meanwhile, if the vehicle is in reverse mode, ie if the selectedposition s of the select lever is “reverse”, the conditions under whichthe content of the brake control signal changes to “on” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the rotational speed nO and torque τO of the output shaftassume negative values (Step 203).

Furthermore, if the vehicle is in neutral mode, that is, if the selectedposition s of the select lever is “neutral”,while the content of thebrake control signal B is “off” and the absolute value of the outputshaft speed nO is lower than the threshold value NO1, a brake controlsignal B with the content “on” is generated (Step 203). This is outputfrom the controller 14 to the brake control actuator 15 (Step 206), andthe brakes 4, 5 are applied automatically (Step 207).

Furthermore, irrespective of the selected position s of the selectlever, if a state wherein the absolute value of the target rotationalspeed NO of the output shaft is smaller than a prescribed thresholdvalue NO2 lasts for more than a prescribed length of time t (sec), abrake control signal B with the content “on” is generated (Step 203).This is output from the controller 14 to the brake control actuator 15(Step 206), and the brakes 4, 5 are applied automatically (Step 207).

Here, the reason for insisting that “the output shaft torque tO isgreater than the prescribed threshold value TO2” as a condition forapplying the brakes automatically is in order to reduce loss resultingfrom the motor drive current when the vehicle does not start within theprescribed time, since the tractive force of the engine is maintainedduring standstill.

Next, if it is assumed that the vehicle is about to start on a slope,the operator depresses the accelerator pedal in order to start thevehicle.

Then, the load torque TO(α) on the output shaft when the brakes are notapplied is calculated on the basis of the acceleration α as detected bythe forward and backward acceleration sensor 11 (Step 204).

Meanwhile, the current torque τO on the output shaft is obtained as theoutput of the output shaft torque sensor 10. If these torques TO(α), τOare compared, and in forward mode the content of the brake controlsignal B is “on”, while the output shaft torque τO is greater than theload torque TO(α) corresponding to the abovementioned acceleration, itis judged the brakes can be released in order for the vehicle to start,whereupon a brake control signal B with the content “off” is generated(Step 205). This is output from the controller 14 to the brake controlactuator 15 (Step 206), and the brakes 4, 5 are released automatically(Step 207). As a result, the operator is able to start the vehicle withsufficient tractive force for the gradient of the slope by means of thesimple operation of depressing the accelerator.

Meanwhile, if the vehicle is in reverse mode, the conditions under whichthe content of the brake control signal changes to “off” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the codes for the torque τO, TO(α) are reversed (Step205).

There now follows, with reference to the control block diagram in FIG.6, a description of the most suitable processing for the vehicleillustrated in FIG. 3.

As may be seen from FIG. 6, to begin with, data from the abovementionedsensors 9, 10, 11, 13, 12, 8 (ie rotational speed nO and torque τO ofthe output shaft, forward and backward acceleration α, selected positions of the select lever, changes in accelerator pedal displacement x,engine rotational speed nE) is introduced item by item into thecontroller 14 (Step 302).

Here, when the target engine rotational speed NE (x) is increasing, amaximum value is set for each time elapsed (t). If the target enginerotational speed NE (x) obtained in Step 302 is in excess of thismaximum value, the maximum value is output, while if the target enginerotational speed NE (x) obtained in Step 302 is less than this maximumvalue, the target engine rotational speed NE (x) obtained in Step 302 isoutput without modification.

Meanwhile, when the target engine rotational speed NE (x) is decreasing,a minimum value is set for each time elapsed (t). If the target enginerotational speed NE (x) obtained in Step 302 is less than this minimumvalue, the minimum value is output, while if the target enginerotational speed NE (x) obtained in Step 302 is in excess of thisminimum value, the target engine rotational speed NE (x) obtained inStep 302 is output without modification.

The target engine rotational speed NE calculated in this manner isoutput to the converter controller 18. As a result, the convertercontroller 18 adjusts the converter 17 while the motor 19 is operatingas a motor, allowing the generator 16 to act as a motor when the motor19 is operating as a generator, and controls the engine in such a mannerthat it attains the target engine rotational speed NE. In this processthe output nE of the engine rotational speed sensor 8 is used as thefeedback amount (Step 309).

Next, a function f with the current engine rotational speed nE outputfrom Step 303, current rotational speed nO of the output shaft, selectedposition s of the select lever and engine rotational speed nE asvariables is used to calculate the target value NO=f (nO, nE, NE, s) ofthe rotational speed of the output shaft of the motor 19. This targetvalue NO assumes a positive value in forward mode and a negative valuein reverse mode. The minimum value NOmin in forward mode and the maximumvalue NOmax in reverse mode are 0.

The target rotational speed NO of the output shaft calculated in thismanner is output to the inverter controller 21 (Step 304). As a result,the motor 19 is controlled via the inverter controller 21 in such amanner that the rotational speed of the motor 19 becomes theabovementioned target rotational speed NO. In this process the output nOof the output shaft rotational speed sensor 9 is used as the feedbackamount (Step 309).

If it is here assumed that the vehicle is ascending a slope and stops inthe course of the slope, the operator releases the accelerator pedal andapplies the brake (depresses the brake pedal) in order to stop thevehicle.

Here, if the vehicle is in forward mode, ie if the selected position sof the select lever is “forward”, while the content of the brake controlsignal B is “off”, the output shaft speed nO is lower than theprescribed threshold value NO, the output shaft torque τO is greaterthan the prescribed threshold value TO1 and the engine rotational speednE is lower than the prescribed threshold value NE1, it is judged thatthe vehicle may be about to stop, and a brake control signal B with thecontent “on” is generated (Step 305). This is output from the controller14 to the brake control actuator 15 (Step 308), and the brakes 4, 5 areapplied automatically (Step 309). As a result, the operator is able tobring the vehicle to a halt on a slope by means of the simple operationof releasing the accelerator, although in order to decrease the speed ofthe vehicle the operator must depress the brake pedal until momentsbefore the vehicle comes to a standstill. Moreover, the vehicle can bekept at a standstill thereafter without the need to continue depressingthe brake pedal.

In Step 305 above, the reason for insisting that “engine rotationalspeed nE is lower than the prescribed threshold value NE1” is that incircumstances such as these it is believed that the operator releasesthe accelerator pedal with the intention of stopping the vehicle, theengine is subject to the load resulting from the uphill slope, and theengine rotational speed is below that of idling. It is thereforepreferable for the abovementioned prescribed threshold value NE1 to bebelow the idling speed.

Meanwhile, if the vehicle is in reverse mode, ie if the selectedposition s of the select lever is “reverse”, the conditions under whichthe content of the brake control signal changes to “on” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the rotational speed nO and torque τO of the output shaftassume negative values (Step 305).

Furthermore, if the vehicle is in neutral mode, ie if the selectedposition s of the select lever is “neutral”, while the content of thebrake control signal B is “off” and the absolute value of the outputshaft speed nO is lower than the threshold value NO1, a brake controlsignal B with the content “on” is generated (Step 305). This is outputfrom the controller 14 to the brake control actuator 15 (Step 308), andthe brakes 4, 5 are applied automatically (Step 309).

Furthermore, irrespective of the selected position s of the selectlever, if a state wherein the absolute value of the target rotationalspeed NO of the output shaft is smaller than a prescribed thresholdvalue NO2 lasts for more than a prescribed length of time t (sec), abrake control signal B with the content “on” is generated (Step 305).This is output from the controller 14 to the brake control actuator 15(Step 308), and the brakes 4, 5 are applied automatically (Step 309).

Next, if it is assumed that the vehicle is about to start on a slope,the operator depresses the accelerator pedal in order to start thevehicle.

Then, the load torque TO(α) on the output shaft when the brakes are notapplied is calculated on the basis of the acceleration α as detected bythe forward and backward acceleration sensor 11 (Step 306).

Meanwhile, the current torque τO on the output shaft is obtained as theoutput of the output shaft torque sensor 10. If these torques TO(α), τOare compared, and in forward mode the content of the brake controlsignal B is “on”, while the output shaft torque τO is greater than theload torque TO(α) corresponding to the abovementioned acceleration, itis judged the brakes can be released in order for the vehicle to start,whereupon a brake control signal B with the content “off” is generated(Step 307). This is output from the controller 14 to the brake controlactuator 15 (Step 308), and the brakes 4, 5 are released automatically(Step 309). As a result, the operator is able to start the vehicle withsufficient tractive force for the gradient of the slope by means of thesimple operation of depressing the accelerator.

Meanwhile, if the vehicle is in reverse mode, the conditions under whichthe content of the brake control signal changes to “off” are the same asthose which apply to forward mode, except for differences resulting fromthe fact that the codes for the torque τO, TO(α) are reversed (Step307).

It is also possible to implement variations on parts of the processesillustrated in FIGS. 4-6, as may be seen for example from FIGS. 7-13.

FIG. 7 illustrates a variation on Step 102 in FIG. 4.

That is to say, if the vehicle is in forward mode, ie if the selectedposition s of the select lever is “forward”, while the output shaftspeed nO is lower than the prescribed threshold value NO1 and graduallydecreasing, or the output shaft speed nO is lower than the prescribedthreshold value NO1 and the output shaft torque τO is smaller than theload torque TO(α) corresponding to the acceleration, it is judged thatthe vehicle may be about to stop, and a brake control signal B with thecontent “on” is generated.

Here, the reason for insisting that “the output shaft torque τO issmaller than the load torque TO(α) corresponding to the acceleration” isthat in circumstances such as these it is believed that the operatorreleases the accelerator pedal with the intention of stopping thevehicle, and as a result the output shaft torque τO is below the torquerequired to overcome forward and backward acceleration (gravity).

The automatic brake is applied under similar conditions when the vehicleis in reverse mode.

FIG. 8 also illustrates a variation on Step 102 in FIG. 4.

That is to say, if the vehicle is in forward mode, ie if the selectedposition s of the select lever is “forward”, while the output shaftspeed nO is lower than the prescribed threshold value NO1 and the enginerotational speed nE is lower than the prescribed value NE1, or theoutput shaft speed nO is lower than the prescribed threshold value NO1and the change in the accelerator displacement x is less than theprescribed value X1, it is judged that the vehicle may be about to stop,and a brake control signal B with the content “on” is generated.

Here, the reason for insisting that “the change in the acceleratordisplacement x is less than the prescribed value X1” is that incircumstances such as these it is believed that the operator releasesthe accelerator pedal with the intention of stopping the vehicle.

The automatic brake is applied under similar conditions when the vehicleis in reverse mode.

FIG. 9 also illustrates a variation on Step 102 in FIG. 4.

That is to say, if the vehicle is in forward mode, ie if the selectedposition s of the select lever is “forward”, while the content of thebrake control signal B is “off”, and a state wherein the output shaftspeed nO is lower than the prescribed threshold value NO1 lasts forlonger than the prescribed time T1, it is judged that the vehicle may beabout to stop, and a brake control signal B with the content “on” isgenerated.

Here, the reason for insisting that “a state wherein the output shaftspeed nO is lower than the prescribed threshold value NO1 lasts forlonger than the prescribed time T1” is that in circumstances such asthese it is believed that the operator releases the accelerator pedalwith the intention of stopping the vehicle.

The automatic brake is applied under similar conditions when the vehicleis in reverse mode.

FIG. 10 illustrates a variation on Step 104 in FIG. 4.

That is to say, if in forward mode the output shaft torque τO is greaterthan the load torque TO(α) corresponding to the acceleration, and theaccelerator pedal is depressed (the displacement x of the acceleratorpedal is greater than zero), it is judged the brakes can be released inorder for the vehicle to start, whereupon a brake control signal B withthe content “off” is generated.

The automatic brake is released under similar conditions when thevehicle is in reverse mode.

FIG. 11 also illustrates a variation on Step 104 in FIG. 4.

That is to say, if in forward mode the output shaft torque τO is greaterthan the load torque TO(α) corresponding to the acceleration, or theaccelerator pedal is depressed (the displacement x of the acceleratorpedal is greater than zero), it is judged the brakes can be released inorder for the vehicle to start, whereupon a brake control signal B withthe content “off” is generated.

The automatic brake is released under similar conditions when thevehicle is in reverse mode.

FIG. 12 illustrates a variation on Step 203 in FIG. 5.

That is to say, if the vehicle is in forward mode, ie if the selectedposition s of the select lever is “forward”, while the output shaftspeed nO is lower than the prescribed threshold value NO1, the outputshaft torque τO is greater than the prescribed threshold value TO1, andlonger than the prescribed length of time T2 has elapsed since thecontent of the brake control signal B changed to off or longer than theprescribed time T3 has elapsed since the absolute value of the outputshaft speed nO has been smaller than the prescribed threshold NO2, it isjudged that the vehicle may be about to stop, and a brake control signalB with the content “on” is generated.

Here, the reason for insisting that “longer than the prescribed lengthof time T2 has elapsed since the content of the brake control signal Bchanged to of” is in order to avoid errors whereby the automatic brakeoperates when the vehicle starts.

The automatic brake is applied under similar conditions when the vehicleis in reverse mode.

FIG. 13 illustrates a variation on Step 305 in FIG. 6.

Here, if the vehicle is in forward mode, ie if the selected position sof the select lever is “forward”, while the output shaft speed nO islower than the prescribed threshold value NO1, the output shaft torqueτO is greater than the prescribed threshold value TO1, and longer thanthe prescribed length of time T2 has elapsed since the content of thebrake control signal B changed to off, longer than the prescribed timeT3 has elapsed since the absolute value of the output shaft speed nO hasbeen smaller than the prescribed threshold NO2, or the output shaftspeed nO is lower than the prescribed value NO1 and the enginerotational speed nE is lower than the prescribed value nE1, it is judgedthat the vehicle may be about to stop, and a brake control signal B withthe content “on” is generated.

The automatic brake is applied under similar conditions when the vehicleis in reverse mode.

INDUSTRIAL APPLICABILITY

The present invention can be applied not only to wheeled vehicles butalso to vehicles which run on crawler tracks.

What is claimed is:
 1. An apparatus for controlling brakes of a vehicle,including the vehicle having an accelerator pedal and a brake pedal, andthe brakes stopping the vehicle by applying frictional force to wheelsof the vehicle, comprising: travelling speed detecting means fordetecting a travelling speed of a vehicle; and control means forcontrollingly actuating the brakes for stopping the vehicle withoutoperating the brake pedal when the travelling speed detected by thetravelling speed detecting means becomes a prescribed threshold value orless by the operation of the accelerator pedal.
 2. An apparatus forcontrolling brakes of a vehicle, including the vehicle having anaccelerator pedal and a brake pedal, and the brakes for stopping thevehicle by applying frictional force to wheels of the vehicle,comprising: travelling speed detecting means for detecting a travellingspeed of the vehicle; and control means for controllingly actuating thebrakes for stopping the vehicle without operating the brake pedal when acurrent travelling speed detected by the travelling speed detectingmeans becomes a prescribed threshold value or less and the currenttravelling speed becomes smaller than a previously detected travellingspeed by the operation of the accelerator pedal.
 3. An apparatus forcontrolling a brake of a vehicle having an accelerator pedal and a brakepedal, comprising: travelling speed detecting means for detecting atravelling of the vehicle; acceleration detecting means for detecting anacceleration of the vehicle in a forward and backward direction; loadcalculating means for calculating a load on an output shaft when thebrake is not applied, on the basis of the acceleration detected by theacceleration detecting means; load detecting means for detecting theload on the output shaft; and control means for controllingly actuatingthe brake when the travelling speed detected by the traveling speeddetecting means becomes a prescribed threshold value or less and a loaddetected by the load detecting means becomes smaller than a loadcalculated by the load calculating means.
 4. An apparatus forcontrolling a brake of a vehicle having an accelerator pedal and a brakepedal, comprising: travelling speed detecting means for detecting atravelling speed of the vehicle; depression detecting means fordetecting a depressed amount of the accelerator pedal; and control meansfor controllingly actuating the brake when the travelling speed detectedby the travelling speed detecting means becomes a prescribed thresholdvalue or less and the depressed amount of the accelerator pedal detectedby the depression amount detecting means becomes a prescribed thresholdvalue or less.
 5. An apparatus for controlling a brake of a vehiclehaving an accelerator pedal and a brake pedal wherein the brake isautomatically actuated and thereafter turned off, comprising:acceleration detecting means for detecting an acceleration of thevehicle in a forward and a backward direction; load calculating meansfor calculating, on the basis of the acceleration detected by theacceleration detecting means, a load on an output shaft while the brakeis not applied; load detecting means for detecting the load on theoutput shaft; and control means for controllingly deactivating the brakewhen the load detected by the load detecting means becomes greater thanthe load calculated by the load calculating means.
 6. An apparatus forcontrolling a brake of a vehicle having an accelerator pedal and a brakepedal wherein the brake is automatically actuated and thereafter turnedoff, comprising: acceleration detecting means for detecting anacceleration of the vehicle in a forward and backward direction; loadcalculating means for calculating, on the basis of the accelerationdetected by the acceleration detecting means, a load on an output shaftwhen the brake is not applied; load calculating means for calculating,on the basis of the acceleration detected by the acceleration detectingmeans, a load on an output shaft when the brake is not applied; loaddetecting means for detecting the load on the output shaft; operationdetecting means for detecting that the accelerator pedal has beenoperated; and control means for controllingly deactivating the brakewhen the load detected by the load detecting means becomes greater thanthe load calculated by the load calculating means and when the operationdetecting means detects that the accelerator pedal has been operated. 7.An apparatus for controlling brake of a motor-driven vehicle having anaccelerator pedal and a brake pedal wherein the brake is automaticallyturned on and off, comprising: travelling speed detecting means fordetecting a travelling speed of the vehicle; load detecting means fordetecting a load on an output shaft of the motor; timer means formeasuring a time since the automatically turned-on-and-off brake wasturned off; and control means for controllingly actuating the brake whenthe travelling speed detected by the travelling speed detecting meansbecomes a prescribed threshold value or less, the load detected by theload detecting means becomes a prescribed threshold value or more andthe time measured by the timer means becomes a prescribed thresholdvalue or more.